Plunge freezing is a technique that cryo immobilizes a very thin film of aqueous solution by rapidly plunging it into liquid ethane or propane. Briefly, a few microliters of the solution of interest is pipetted onto a 3mm diameter electron microscope grid. The solution is then blotted for a few seconds to remove all but a thin film of the solution. The grid, suspended by tweezers, is immediately plunged into a reservoir of liquid ethane. This technique produces a thin layer of the solution preserved in vitreous ice. The sample can then be studied in its native state in the electron microscope under cryo conditions. Of concern to the scientist during this procedure is the ionic transport and subsequent elevated osmotic pressure in cells that might result just after the blotting procedure. Because only a thin film remains after the blotting, any evaporation causes concentration of the residual sample. Some molecular and biological sample solutions are also remarkably effected by changes in temperature. To obviate these problems an environmental chamber is under development to control both humidity and temperature of the sample until it is plunged into the liquid ethane. A prototype of the device has been designed and built and is being tested under laboratory conditions.